Field of the Invention
The present invention relates to a burner port block assembly for conveying the heat and hot gases from a burner to a furnace. More specifically, the invention is directed to a burner port block assembly having a ceramic insert and a reduced size refractory block.
Description of Related Art
Direct fired burners, where the flame, heat, and products of combustion are fired directly into the furnace atmosphere, have been used since the 1960's, especially in the direct-fired section of strip galvanizing line preheaters. Between the burner and the furnace wall is a port block, also known as a tile or a quarl, through which the flame, heat, and hot gases pass into the furnace. In many applications, including “non-oxidizing” or “NOF” furnaces, the port block runs unusually hot and can reach surface temperatures in excess of 2800° F.
Historically, the walls of this type of furnace were lined with firebrick. Thus, the furnace wall heat storage capacity was quite high, causing the furnaces to heat up and cool down slowly. Port blocks made of 3000° F. or better material would normally retain their structural integrity in service for at least as long as the lining of the furnace walls.
Some users of this type of furnace have begun lining the furnace walls with fiber linings instead of furnace brick. This allows the furnace to be heated and cooled much more quickly, giving more operating flexibility. However, the castable monolithic refractory port blocks become a weak point in this type of operation. In general, the thick monolithic refractory port blocks are not well suited for rapid thermal cycling, especially rapid cool-down, and tend to crack and fall apart under these conditions.
While this problem has been known for at least 10 years, no suitable solution has been found. Many studies have been commissioned to study the thermal shock failure of the monolithic refractory port blocks without a successful solution being identified. Thus, a port block is needed that will withstand the rapid heating and cooling experienced in these fiber lined furnaces without significant degradation.